Microstructural evolution and oxide layer structure of C_sf/SiBCN composites during oxidation at 1500 ℃

The microstructural evolution of C_sf/SiBCN composites and formation mechanism of the oxide layer after oxidation for 1–10 h at 1500 ℃ were studied. As the oxidation time increases to 10 h, the macrostructure of the porous C_sf/MA-SiBCN composite collapses obviously, while the C_sf/SiBCN composite densified via the polymer infiltration and pyrolysis (PIP) process maintains structural integrity due to the formation of the oxide layer with a tri-layer structure: the outermost loose layer mainly containing cristobalite, the dense interlayer of amorphous glass and the innermost layer of some unoxidized BN(C) and SiC grains embedded into the amorphous glass, which hinders the diffusion of oxygen.